A tape player in general takes different operational modes such as a play mode, fast-forwarding (FF) mode, rewinding (REW) mode, stop or pause mode, and loading/ejection mode. These modes require different positions of a head with respect to a tape. Therefore, such a head is supported on a head plate moved by a drive means in a direction perpendicular to the tape running direction so as to bring the head to and away from the tape.
An arrangement for driving the head plate is configured to convert rotation of a motor to a linear power by a cam intermittently rotated only when the head plate is to be driven, and uses the linear power to move the head plate.
FIG. 4 shows a prior art arrangement of a driving means of this type.
An intermittent gear 81 is mounted adjacent a drive gear 80 which is continuously rotated by a motor. The intermittent gear 81 has a cutout 82 partly breaking a series of circumferential gear teeth thereof and has a cam 83 integrally formed on one surface thereof. A linearly reciprocal power plate 84 is mounted adjacent the intermittent gear 81 and has a roller 85 contacting the outer margin of the cam 83. Therefore, with rotation of the intermittent gear 81, the power plate 84 is guided and linearly moved by the cam 83.
The power plate 84 has a pin-shaped pull member 86 engageable with an engage portion 88 formed on a shift plate 87 co-movable with the head plate. When the power plate 84 moves, the pull member 86 compressively engages the engage portion 88b and moves the shift plate 87 ahead (rightwardly) together with the head plate. The shift plate 87 is rotatable about a junction 89 joining it to the head plate. However, since a holding means not shown prevents the shift plate 87 from rotating during advance movement of the head plate, the pull member 86 applies a linear power to the engage portion 88.
When the shift plate 87 reaches its advance position and is locked by a lock means 90, the contact point of the cam 83 with respect to the roller 85 moves to a smaller radius portion, and the power plate 84 starts withdrawal. With a slight withdrawal of the power plate 84, the cutout 82 of the intermittent gear reaches the drive gear 80, and the intermittent gear 81 loses the driving energy. If the intermittent gear 81 is locked immovable there, the power plate 84 also stops, and the head plate completes its advance. Therefore, the power plate 84, when brought to this position, is locked there by a specifically provided lock member 91. This lock of the power plate 84 is effected at a position where the roller 85 stops at an angled portion slightly backward of the smallest radius portion of the cam 83.
In withdrawal of the head plate, the shift plate holding means is released by a plunger, for example, to detach the shift plate 87 from the lock means 90 and allow the shift plate 87 and head plate to withdraw with the energy of a revival spring.
In a re-advance of the head plate, the lock member 91 is unlocked by a plunger, for example. The power plate 84 is allowed to withdraw with the energy of a revival spring, and the roller 85 compressively moves along the cam 83 up to the smallest radius portion. The compression force of the roller 85 causes the intermittent gear 81 to slightly rotate together with the cam 83 so that one end portion of the series of teeth of the intermittent gear 81 engages the drive gear 80. This initial engagement between the intermittent gear 81 and drive gear 80 is hereinafter called "priming engagement". After the priming engagement is established, the rotation of the drive gear 80 is transmitted to the intermittent gear 81, cam 83, power plate 84 and shift plate 87 in this order, and the head plate is moved ahead.
In order to lock the power plate at a position ready for establishing the priming engagement which is indispensable for control of back and forth movement of the head plate, the prior art mechanism employs a specific lock member 91 controlled by a plunger.
The specific use of the lock member 91 increases the number of parts of the mechanism and hence invites a complicated structure and an increase of the assembling process. Additionally, the prior art arrangement requires two plungers for control of the head plate because the plunger for control of the shift plate holding means is deenergized upon withdrawal of the head plate, and a further plunger is used to unlock the power plate lock member.